CVE-2025-4918 — An attacker was able to perform an out-of-bounds read or write on a JavaScript `Promise` object.

Description

An attacker was able to perform an out-of-bounds read or write on a JavaScript `Promise` object. This vulnerability was fixed in Firefox 138.0.4, Firefox ESR 128.10.1, Firefox ESR 115.23.1, Thunderbird 128.10.2, and Thunderbird 138.0.2.

References

• https://bugzilla.mozilla.org/show_bug.cgi?id=1966612
• https://www.mozilla.org/security/advisories/mfsa2025-36/
• https://www.mozilla.org/security/advisories/mfsa2025-37/
• https://www.mozilla.org/security/advisories/mfsa2025-38/
• https://www.mozilla.org/security/advisories/mfsa2025-40/
• https://www.mozilla.org/security/advisories/mfsa2025-41/
• https://lists.debian.org/debian-lts-announce/2025/05/msg00024.html
• https://lists.debian.org/debian-lts-announce/2025/05/msg00046.html
• https://www.vicarius.io/vsociety/posts/cve-2025-4918-detect-firefox-out-of-bounds-write
• https://www.vicarius.io/vsociety/posts/cve-2025-4918-mitigate-firefox-out-of-bounds-write